CR and SCR methods are increasingly used with camera traps for rare and elusive carnivores that are difficult to monitor with traditional methods (Dillon, 2005; Gerber et al., 2012), and camera traps yield CT capture data that are appropriate for CT models. The CT single-catch trap estimator that is developed in this research is appropriate for single-catch trap data with observed capture times.
Jaguars are an example of a large carnivore that is notoriously difficult to study and possums are the type of small mammal that are often live-trapped with cage traps. The models that are developed in this research are therefore applied to two quite different datasets, one from a camera trap survey of jaguars and the other from a live-trapping study of possums where timing devices were fixed to the cages.
1.5.1
Jaguars in Belize
Jaguars (Panthera onca) are near threatened and their global population is declining (Caso et al., 2008), and population monitoring is difficult because they occur at low densities, range widely and are elusive, often inhabiting thick habitat. Over the past decade, the challenge of detecting jaguars for population estimation has been facilitated by camera traps, following the work of Silver et al. (2004); however, reliable and robust density estimates of jaguars are rarely obtained (see Foster and Harmsen, 2012; Tobler and Powell, 2013).
Study site and camera trapping of jaguars
The Cockscomb Basin Wildlife Sanctuary in Belize encompasses 490 km2 of sec- ondary tropical moist broadleaf forest at various stages of regeneration following anthropogenic and natural disturbance (for more details see Harmsen et al., 2010b). To the west, the sanctuary forms a contiguous forest block with the protected forests of the Maya Mountain Massif (≈ 5,000 km2 of forest). To the east the sanctuary is
partially buffered by unprotected forest beyond which is a mosaic of pine savannah, shrub land and broadleaf forest, inter-dispersed with villages and farms. Jaguars are found throughout this landscape (Foster et al., 2010). There are 65 km of trails, all within the eastern part of the sanctuary (see Figure 1.1 and Figure 1.2).
Few female jaguars were detected and since females have very different home ranges and possibly density, the analyses only use male detections. Male jaguars routinely walk the trail system and trail use overlaps extensively. Although they frequently leave the trails to move through the forest they are rarely detected off- trail by camera traps (Harmsen et al., 2010a). Nineteen paired camera stations
Camera stations Trails Protected areas Forest 10 km 0 MEXICO GUATEMALA BELIZE COCKSCOMB BASIN WILDLIFE SANCTUARY
(Pantheracam v3) were deployed along the trail network within the eastern basin and maintained for 90 days (April to July 2011) producing 207 captures of 17 individuals. Neighbouring stations had an average spacing of 2.0 km (1.1 to 3.1 km). Digital photographic data were downloaded every two weeks.
1.5.2
Brushtail possums in New Zealand
Possums (Trichosurus vulpecula) were introduced to New Zealand in the nineteenth century to establish a fur industry (Efford and Cowan, 2004). Their selective brows- ing and predation on indigenous birds and invertebrates has caused them to become major pests (Campbell, 1990; Sadleir, 2000).
Study site and trapping of possums
The study site is in a mixed podocarp-hardwood forest in Orongorongo Valley on the North island of New Zealand (for more details see Efford and Cowan, 2004; Cowan and Forrester, 2012). Possums were live-trapped in a grid of wire mesh cage traps spaced 30 meters apart from each other that were baited with pieces of apple coated in flour and mixed with aniseed oil. The trapping ran for three consecutive days each month and traps were checked and reset daily.
The trapping grid is bounded to the north and west by the Orongorongo River. Apart from the river the habitat surrounding the trapping grid for several kilometers is similar to that covering the grid. Figure 1.2 shows the study area used in the pos- sum analysis which has the river and the area across the river excluded as potential areas where activity centres could occur.
Timing devices (accurate to within five minutes) were fitted to the door frames of the traps and were activated when the door closed. Occasionally other non-targeted species such as rats (Rattus rattus), mice (Mus musculus) and hedgehogs (Erinaceus
europeus) triggered the traps. In these cases the timing devices still recorded the
time that the trap was triggered and these events are referred to as “DG” events (door Down and bait Gone).
In this population females breed once a year in May - June, young become in- dependent during October to December, and juvenile dispersal occurs mostly from February to April but can happen from December to May. There may also be some additional movement of animals during the mating period (April-June) (Cowan, per- sonal communication, 2015). In order to maintain the assumption of a closed pop- ulation, the months of August, September and October (from 1982) are selected for analysis. The data were received in hand written timing sheets (see Figure 1.3) and were transcribed and formatted appropriately for analysis. From August to Octo- ber 70 unique possums were trapped over 57 cage traps and there were 286 capture events. Trap saturation can be calculated as the average proportion of traps that are occupied at the end of an occasion, and in these data the average trap saturation was 58%.